Composite pianos are known in which an electronic sound source is combined with an acoustic piano. The composite piano can be played both in a normal piano performance mode in which the hammers strike the strings to produce sound, and in an electronic performance mode in which sound is produced by operating the electronic sound source. When such a composite piano is played in the electronic performance mode, the hammer striking sound is prevented by a stop rail that acts as a damper. When the hammer attached to the tip of a hammer shank is about to strike a string, the movement of the hammer shank is checked by the stop rail.
In the normal piano performance mode, the hammer stop rail of the damper unit needs to be positioned in a retracted position where the hammer stop rail does not contact the hammer shanks, thereby allowing the hammers to strike the strings. For this purpose, as shown in FIG. 6, a conventional prior art stop rail support arm 91 is extended from the lower edge of a hammer stop rail 90. The lower end of stop rail support arm 91 is secured to a support shaft 94 extending parallel with a rotary shaft 93 on which a hammer shank 92 pivots. By operating a lever 95 for rotating the support shaft 94, the hammer stop rail 90 is positioned at a stop position, shown by solid lines, where the motion of the hammer shanks 92 is halted by the rail 90 or at a retracted position, shown by dotted lines, where the hammer stop rail 90 does not contact the hammer shanks 92.
In the conventional damper unit, however, when the hammer stop rail 90 is positioned at the stop position or at the retracted position, the shaft 94 supporting the stop rail arm 91 is rotated by directly operating the lever 95 in the directions shown by an arrow. As a result, a relatively large drive force is required for changing the position of the hammer stop rail 90.
Moreover, when the hammer stop rail contacts the hammer shanks at the stop position, the resulting impact causes the support shaft to rotate toward the retracted position and the stop position of the hammer stop rail deviates. The deviation of the stop position of the stop rail 90 toward the retracted position results in unintentional hammer strikes on the strings. Therefore, the string striking sound cannot be effectively and reliably dampened.